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Medical Physics / Volume 38 / Issue 12 / RADIATION MEASUREMENT PHYSICS

Med. Phys. 38, 6763 (2011); http://dx.doi.org/10.1118/1.3664007 (12 pages)

A new water-equivalent 2D plastic scintillation detectors array for the dosimetry of megavoltage energy photon beams in radiation therapy

Mathieu Guillot, Luc Beaulieu, Louis Archambault, and Luc Gingras

Département de Physique, de Génie Physique et d’Optique, Université Laval, Québec, Québec G1K 7P4, Canada and Département de Radio-Oncologie, Hôtel-Dieu de Québec, Centre Hospitalier Universitaire de Québec, Québec, Québec G1R 2J6, Canada

Sam Beddar

Department of Radiation Physics, Unit 94, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, Texas 77030

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(Received 11 July 2011; accepted 7 November 2011; revised 6 October 2011; published online 30 November 2011)

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Purpose: The objective of this work is to present a new 2D plastic scintillation detectors array (2D-PSDA) designed for the dosimetry of megavoltage (MV) energy photon beams in radiation therapy and to characterize its basic performance.
Methods: We developed a 2D detector array consisting of 781 plastic scintillation detectors (PSDs) inserted into a plane of a water-equivalent phantom. The PSDs were distributed on a 26 × 26 cm2 grid, with an interdetector spacing of 10 mm, except for two perpendicular lines centered on the detection plane, where the spacing was 5 mm. Each PSD was made of a 1 mm diameter by 3 mm long cylindrical polystyrene scintillating fiber coupled to a clear nonscintillating plastic optical fiber. All of the light signals emitted by the PSDs were read simultaneously with an optical system at a rate of one measurement per second. We characterized the performance of the optical system, the angular dependency of the device, and the perturbation of dose distributions caused by the hundreds of PSDs inserted into the phantom. We also evaluated the capacity of the system to monitor complex multileaf collimator (MLC) sequences such as those encountered in step-and-shoot intensity modulated radiation therapy (IMRT) plans. We compared our results with calculations performed by a treatment planning system and with measurements taken with a 2D ionization chamber array and with a radiochromic film.
Results: The detector array that we developed allowed us to measure doses with an average precision of better than 1% for cumulated doses equal to or greater than 6.3 cGy. Our results showed that the dose distributions produced by the 6-MV photon beam are not perturbed (within ±1.1%) by the presence of the hundreds of PSDs located into the phantom. The results also showed that the variations in the beam incidences have little effect on the dose response of the device. For all incidences tested, the passing rates of the gamma tests between the 2D-PSDA and the treatment planning system were higher than 97.5% when the standard clinical tolerances of 3% or 3 mm were used. Excellent agreement was obtained between the doses measured and calculated when we used the 2D-PSDA for monitoring a MLC sequence from a step-and-shoot IMRT plan.
Conclusions: We demonstrated the feasibility of using a large number of PSDs in a new 2D-PSDA for the dosimetry of MV energy photon beams in radiation therapy. The excellent precision, accuracy, and low angular dependence of the device indicate that such a prototype could potentially be used as a high-accuracy quality assurance tool for IMRT and arc therapy patient plan verification. The homogeneity and water-equivalence of the prototype we built suggest that this technology could be extended to multiple detection planes by arranging the fibers into more complex orientations, opening the possibility for 3D dosimetry with PSDs.

© 2011 American Association of Physicists in Medicine

ACKNOWLEDGMENTS

This work was supported by grants from the Natural Sciences and Engineering Research Council (NSERC) (Discovery Grant No. 262105). Mathieu Guillot is financially supported by a NSERC postgraduate scholarship. The authors are grateful to Frédéric Lacroix for providing expertise with radiochromic films.

Article Outline

  1. INTRODUCTION
  2. MATERIALS AND METHODS
    1. The detector array
    2. The optical system
    3. Image processing
    4. Calibration
    5. Characterization of the optical system
    6. Characterization of the angular dependence
    7. Characterization of the water-equivalence
      1. CT of the 2D-PSDA
      2. Dose measurements
    8. Time-resolved measurement of a MLC sequence
  3. RESULTS
    1. Characterization of the optical system
    2. Characterization of the angular dependence
    3. Characterization of the water-equivalence
      1. CT of the 2D-PSDA
      2. Dose measurements
    4. Time-resolved measurement of a MLC sequence
  4. DISCUSSION
  5. CONCLUSIONS
Digital Object Identifier
http://dx.doi.org/10.1118/1.3664007

KEYWORDS and PACS

Keywords

biomedical equipment, dosimetry, phantoms, radiation therapy, solid scintillation detectors, plastic scintillation detectors, detector array, IMRT, water-equivalence, angular dependence

PACS

PUBLICATION DATA

ISSN

0094-2405 (print)  

Publisher

$abstract.society.value is a Member of CrossRef American Association of Physicists in Medicine

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